Answer: Your jpeg files are great for anything you do on the web, but when it comes to printing, a jpeg is not the answer.
Next time you pay your designer to create your artwork, make sure that you ask for all of their workers and a print ready PDF as well. If it is not their policy to do this, then you may have chosen the wrong designer. You may not be able to open these files with the programs that you have, but that does not mean that these files are unimportant or corrupt. Hang on to all of these files in a safe place and when you are ready to print, you will be glad that you did, and you will have them to hand off to your printer when you need them. This will save you more headaches than you can begin to imagine, and will also avoid you from being held hostage by your designer, and being forced to go back to them weather you want to or not. This situation is more common than you may think.